1. Technical Field
The present invention relates to motor controlling methods, motor controlling devices, original reading apparatuses, and storage media having program stored thereon.
2. Related Art
Hitherto, various motors such as DC (direct current) motors and stepping motors have been used in devices such scanners and printers. For example, motors such as a motor for paper feeding and a motor for transporting a carriage in which a print head is fitted are provided in printers (see JP-A-2001-219613, for example).
In the aforementioned devices, it is desired to cause the motors to rotate at an extremely slow speed. This is because in a scanner for example, by causing the carriage transport motor to rotate at an extremely low speed (ultra low speed) and move the reading position of an image sensor fitted on the carriage at an extremely low speed, the reading resolution can be increased.
In this regard, in order to achieve ultra low speed motor driving, consideration has been given to employing a technique in which the motor is driven in a condition that the voltage applied thereto is lowered for example each time an output signal, which is outputted by an encoder or the like, is detected. However, there is a problem with this technique involving an initial duty at startup when the motor starts up from a state in which it is stopped.
That is, when the initial duty is high, which is unsuitable for the aforementioned ultra low speed control, the motor goes too far and cannot stop at a targeted stopping position (overshooting of the stopping position occurs). When this happens, the image sensor does not read the original at the intended target position but rather carries out reading of the original at a position overshot from the target position by a specific amount. In this case, a so-called “jaggy” phenomenon becomes undesirably conspicuous.
And conversely to this, when the initial duty is too low for the aforementioned ultra low speed control, the motor cannot reach the target position within the targeted time (the driving time in which the motor is driven is undesirably exceeded). In this case, a so-called dark current accumulates undesirably in the image sensor until the target position is reached, and the image sensor goes into a state in which a charge accumulation time is excessively exceeded (overcharging occurs). In this case, changes due to color irregularity occur before and after the reading by the image sensor.
For this reason, it is desired to drive the motor using an appropriate initial duty in order to improve the image quality in reading originals.